
import { Observable } from 'rxjs';
import { windowCount as higherOrder } from 'rxjs/operators';

/**
 * Branch out the source Observable values as a nested Observable with each
 * nested Observable emitting at most `windowSize` values.
 *
 * <span class="informal">It's like {@link bufferCount}, but emits a nested
 * Observable instead of an array.</span>
 *
 * <img src="./img/windowCount.png" width="100%">
 *
 * Returns an Observable that emits windows of items it collects from the source
 * Observable. The output Observable emits windows every `startWindowEvery`
 * items, each containing no more than `windowSize` items. When the source
 * Observable completes or encounters an error, the output Observable emits
 * the current window and propagates the notification from the source
 * Observable. If `startWindowEvery` is not provided, then new windows are
 * started immediately at the start of the source and when each window completes
 * with size `windowSize`.
 *
 * @example <caption>Ignore every 3rd click event, starting from the first one</caption>
 * var clicks = Rx.Observable.fromEvent(document, 'click');
 * var result = clicks.windowCount(3)
 *   .map(win => win.skip(1)) // skip first of every 3 clicks
 *   .mergeAll(); // flatten the Observable-of-Observables
 * result.subscribe(x => console.log(x));
 *
 * @example <caption>Ignore every 3rd click event, starting from the third one</caption>
 * var clicks = Rx.Observable.fromEvent(document, 'click');
 * var result = clicks.windowCount(2, 3)
 *   .mergeAll(); // flatten the Observable-of-Observables
 * result.subscribe(x => console.log(x));
 *
 * @see {@link window}
 * @see {@link windowTime}
 * @see {@link windowToggle}
 * @see {@link windowWhen}
 * @see {@link bufferCount}
 *
 * @param {number} windowSize The maximum number of values emitted by each
 * window.
 * @param {number} [startWindowEvery] Interval at which to start a new window.
 * For example if `startWindowEvery` is `2`, then a new window will be started
 * on every other value from the source. A new window is started at the
 * beginning of the source by default.
 * @return {Observable<Observable<T>>} An Observable of windows, which in turn
 * are Observable of values.
 * @method windowCount
 * @owner Observable
 */
export function windowCount<T>(this: Observable<T>, windowSize: number,
                               startWindowEvery: number = 0): Observable<Observable<T>> {
  return higherOrder(windowSize, startWindowEvery)(this) as Observable<Observable<T>>;
}
